Compensator for variations of plate currents



A. J. ROHNER COMPENSATOR FOR VARIATIONS 0F PLATE CURRENTS Filed June 1, 192.3

May 25, 1937. 2,081,713

ATTORNEY Patented May 25, 1937 UN-iTED STATES PATENT OFFICE COMPENSATOR FOR VARIATIONS F PLAT CURRENTS i Arnold J. Rohner, Haddon Heights,.N J., assignor to Radio Corporation of America,y a corporation of Delaware Application June 1, 1933, Serial No. 673,885

6 Claims.

The present invention relates to amplifiersand the like andv particularly to amplifiers utilizing thermionic tubes energized: from commercially available alternating current. In' such systems the alternating! current is rectified and filtered before it' is supplied to the grid and anode' elec-- trodesofthe' tubes. However, it iscustomary to supplyv the heater circuits for the cathodes of from the samesource it is seen that variations` of one potential to `controlthe amplification characteristics of'` the tubewill' obviously' aiTect thev aggregate loady on the common` source with the' resulty that the" potentials supplied to the other electrodes therefrom vare caused to vary,

and aerectier tube is used' to rectify the alternating current, it is obvious that theV total"r current drawn-r from the'A rectifier circuiti' willv Vary;

I-n cert'ain'- types of sets, especially precision receivers whereinl the values of the potentials applied? to the elements off" the tubes are critical',

itis-.obvious that' even: the small changes resulting from the aforesaid amplification varying means cannot be tolerated.

It' is an object of the present invention to* devise a system wherein the voltage applied toV any one or more electrodesY of? an electronic tube or tubesmay be variedwithout appreciabl'y affecting the potentials on the other electrodes thereof.

In accordance with the invention the total current drawn from the powersupply circuit is maintained constant irrespective of changes of the control grid bias and/or the auxiliary grid potential' for volume control purposes-by that a' so-called'i'vari'able bleeder circuit is employed. The bleeder circuit is connected across the rectiii'er' output circuit and is arranged' sov as to compensate for' changes in the plate current drawn' by the amplifier tube or` tubes and' thus maintain the total load on the rectifier constant.

It is a further object Yof the present invention to operate' the variable bleederr circuit by the same means" as is used to operate the volume controlz device' of ther receiver, variations iny the amplification factor of the tube being controlled witli-r` respect toA the Variations caused inthe bleeder circuit in such av way that the current through the bleeder circuit increases as the plate 60 current decreases and Vice Versa.

Other objects of the present invention' will' be apparent from the following: detailed specification wheniread` in conjunctionvwith'- the appended drawing wherein,

Figure l represents in diagrammatic formi a prefer-red form ofV the inve'i'ii'iionv as embodied in. an ampliiier wherein the amplification characteristics thereof` are varied by means of changing the potential applied to an auxiliary electrode of the amplifier tubes;

Figure 2 is a curve sheet used to explain certainV features of.' the invention in connectionV with the system shown in Figure l;

Figure 3 represents indiagrammatic forml a circuit arrangement wherein the invention isY employed' in a system utilizing thermionic tubes, the amplificationcharacteristics' ofwhich are varied by changing the control grid* bias potentials; and,

Figure 4 is a curve sheet used to explain the characteristics of the system shown in Figure 31. In Fig-urel 1, terminals I-v and 2 are the usual terminals for connecting the tubes of a receiver yor the like to a power supply' system; It is to be understood that the power supply system may: comprise a rectifier either of the fulll Wave or hal-f Wave type' 'and' lter circuit in which case7 the terminals I and 2 are connected tothe` outfput terminals' of the usual filter circuit. It is to be understood that the line connected to terminal I is the positive conductor, whereas, the liner connected to-terminal 2 is the negative conductor. Two: tubes I4 and I6l which are rep'- reserita-tive` of an amplier arrangement are shown connected to the power supply' system.

While tubes I4 and Iii have been'V showngen-- erally' as' screen grid tubes it isV to be understood that any tube capable of having its character-v istics changed by' varying the potential appliedt'o' onel or more electrodes thereof may' be employed.

It is obvious from'A the drawing that' the ano'd'es ofv the'twotubes 14'- and I6 are connected to thel positive conductor, whereas, one side of the equi-potential cathode of each tubeis connected to the' negative side. The4 heater circuits' for the cathodes have not been shown, however, it is intended that the usual type heater circuit be employed.

vious that by varying the position oi the tap I on the resistance 6 the potential applied to the auxiliary electrodes I 5 and Il may be varied thereby varying the ampliiication characteristics of the tubes Ii and I6. The bleeder circuit comprises a variable resistance I I and a fixed resistance I2 shunted across the conductors I8 and I9 through a `variable tap I3 associated with the resistance I I. Tap I 3 is for the purposes of varying the value oi the resistance I I which is placed in series with resistance I2 across the line. It should be noted that the lower point I0 of the resistance I2 is grounded. A uni-control means represented generally at I8 is arranged so as to allow simultaneous adjustments of the two variable elements l and I3. The system is arranged so that as the screen voltage is increased by moving tap l upwardly along the resistance 6 the plate current would normally increase; however, by means of the mechanical connection 8 to the variable element I3 more resistance II is cut in to the circuit 5, iii with the result that the current through path 9, I@ decreases thereby maintaining the load across the terminals I, 2 substantially constant.

Referring noW to Figure 2, the curve denoted by plate current shows that the plate current through the tubes increases as the screen grid voltage increases, that is, becomes more positive with respect to the cathode. At the same time, the bleeder current decreases, hence, the load placed on the rectifier circuit is substantially constant as is shown by the bleeder and plate current operation of the system shown in Figure 3. It isr obvious from Figure 4 that as the negative grid bias increases the plate current normally decreases. However, through the mechanical inter-connection between taps 2l and 23 the bleeder current increases, hence, the total load across the terminals I and 2 is maintained substantially constant as is shown by the bleeder and plate current curve of said Figure 4.

It is to be understood that the scope of the present invention is to be limited only by the prior art and the scope of the appended claims and not by the particular embodiments shown herein.

I claim:

1. In combination with a space discharge device provided with anode, cathode and grid electrodes, a source of space current for said device, an impedance in series with said source, a variable tap on said impedance and a connection between said tap and a grid electrode of said device, a variable bleeder resistance shunted across said source provided with a controlling element and a common mechanism associated with both said variable tap and the controlling element to permit simultaneous adjustment of both the tap and the element.

2. In combination with a source of current, a

load circuit therefor comprising a pair of variable conductance paths connected in parallel with respect to the source, one of said paths comprising the space path of a space discharge device, separate means for varying the conductance of each of said paths, one of said last named means including said source of current, and a single element common to each of said separate means for simultaneously operating said separate means and arranged so as to vary the conductance oi each of said paths with respect to the other thereof in substantially equal increments but in opposite sense to thereby maintain the load across said source due to said load circuit substantially constant despite variations in said conductances.

3. In an amplier circuit, a space discharge device provided with anode, cathode and grid electrodes, a source of space current for said device,

means for varying the amplification characteristics of said device by controlling the flow of space current through said device, a bleeder circuit connected across said source, means for controlling the flow of current through said bleeder circuit, a common element associated with both said last named means to permit simultaneous operation thereof in a sense to maintain constant the load on said source despite variations in the flow of space current through said device.

4. In combination with an amplier including a plurality of space discharge devices, a source of current for energizing said devices, means for varying the amplification characteristics of said amplifier whereby the current taken by said devices from said source is varied, an auxiliary load circuit associated with said source and means for simultaneously varying the loading characteristics of said auxiliary circuit with variations in the ampliiication characteristics of the ampliiier in a sense to maintain the total load on said source substantially constant.

5. In an amplifier circuit a space discharge device provided With anode, cathode and grid electrodes, a source of space current for said device, means for varying the amplification characteristics of said device by varying the potential applied to one of the electrodes thereof, a bleeder circuit connected across said source, means for controlling the flow of current through the bleeder circuit, and a common element connected with both said last named means to permit simultaneous operation thereof in a sense to maintain constant the load on the source despite variations in the flow of space current through said devices due to variations in the amplification characteristics thereof.

6. In combination with a source of current, a variable impedance shunted across the source, said impedance being provided with a controlling element, a second impedance shunted across the source comprising the space path of an electronic tube, said tube being provided with a control elecj trode, a resistance device in series with the source and the space path of the tube, a variable tap on said resistor device, a connection from said grid to said tap and a common means connected with both said controlling element and said variable tap to permit simultaneous adjustment of both thereof to vary the amplication characteristics of the electronic tube and at the same time maintain the load across the source substantially constant.

ARNOLD J. ROI-INEE. 

